Semiconductor apparatus for power supply control and output voltage variable power supply apparatus

ABSTRACT

A power supply control apparatus includes a voltage control transistor connected between a DC voltage input terminal and an output terminal; a control circuit controlling the voltage control transistor according to an output feedback voltage; and a first external terminal receiving an output control signal to control an output voltage. The control circuit includes a first error amplifier outputting a voltage according to an electric potential difference between a voltage divided by a first voltage dividing circuit which divides the output voltage of the output terminal and a predetermined reference voltage; and an output changing circuit including a second error amplifier receiving a voltage input in the first external terminal, a transistor having a control terminal receiving the output of the second error amplifier, and a current mirror circuit connected to the voltage input terminal which transfers an electric current flowing in the transistor. The output changing circuit displaces the divided voltage according to a voltage input at the first external terminal to change the output voltage according to the output control signal.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional application of U.S. application Ser.No. 16/352,765, filed on Mar. 13, 2019, which is based upon and claimsthe benefit of priority from the prior Japanese Patent Application No.2018-071817, filed Apr. 3, 2018 and Japanese Application No.2018-247303, filed Dec. 28, 2018, the entire contents all of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a DC power supply apparatus and relatesto a useful technique used in a semiconductor apparatus for power supplycontrol which is a series regulator type in which output voltage can bechanged linearly and an output voltage variable power supply apparatus.

DESCRIPTION OF THE RELATED ART

There is a series regulator (hereinafter referred to as a regulator)which is used as a power supply apparatus in which a transistor providedbetween a DC voltage input terminal and output terminal is controlled tooutput a DC voltage in a predetermined potential. The purpose of use forsuch regulator may be a constant voltage power supply apparatus (carmounted regulator) to supply DC current to an electronic device providedin a vehicle, for example, a ventilating device (fan), an illuminatingdevice or an audio device mounted on a body of an automobile.

In an electronic device such as a ventilating device (fan) or anilluminating device, there may be a demand to provide a function inwhich the voltage which drives a motor rotating the fan or which drivesa lamp of the illuminating device is changed linearly to be able tocontinuously change the amount of ventilation or the brightness of theillumination. Therefore, there is a demand that the regulator includes afunction in which the output voltage can be changed linearly.

Conventional inventions showing regulators in which the output voltagecan be changed is described in Japanese Patent Application Laid-OpenPublication No. H11-265224 and Japanese Patent Application Laid-OpenPublication No. 2010-055490, for example.

According to the regulator described in Japanese Patent ApplicationLaid-Open Publication No. H11-265224, a plurality of resistors connectedin series as a voltage dividing circuit which divides the output voltageto generate the feedback signal, and a switch transistor connectedparallel with these resistors are provided, and any of the switchtransistors may be conducted by voltage setting input to change thevoltage dividing ratio. With this, the output voltage is changed.

The output voltage can be switched in stages in the regulator accordingto the above invention but the output voltage cannot be changedlinearly. The number of resistors in series included in the voltagedividing circuit and the number of switch transistors may be increasedto approximately change the output voltage linearly. However, accordingto the above, the number of elements increases and the square areanecessary for mounting the elements increases. Therefore, it becomesdifficult to make the apparatus smaller.

Japanese Patent Application Laid-Open Publication No. 2010-055490describes a variable output voltage regulator in which the outputvoltage is adjusted by including a voltage controller including avoltage monitoring circuit which monitors adjustment resistor elementsand output voltage provided between both terminals of one resistor inseries included in an output voltage dividing circuit to generatefeedback voltage to a linear regulator.

However, the regulator according to the above invention configures anadjustment circuit of the output voltage value with an externallyattached element of the regulator IC. The number of components includedin the apparatus increases, and the square area necessary to mount thecomponents becomes large. Consequently, it becomes difficult to make theapparatus smaller and the consumed electric power increases. Moreover,the amount of power consumed becomes large. Further, the output voltageis varied due to the variation in the resistance value of the adjustmentresistor elements being used. Therefore, the accuracy of the outputvoltage decreases.

SUMMARY OF THE INVENTION

The present invention is conceived in view of the above problems, andthe object of the present invention is to provide a semiconductorapparatus for power supply control and an output voltage variable powersupply apparatus with which the output voltage can be changed linearlywithout increasing the number of elements and components.

Another object of the present invention is to provide a semiconductorapparatus for power supply control and an output voltage variable powersupply apparatus with a high output voltage accuracy.

Another object of the present invention is to provide a semiconductorapparatus for power supply control and an output voltage variable powersupply apparatus which are able to easily control output voltage using ageneral purpose microcomputer.

According to one aspect of the present invention, a semiconductorapparatus for power supply control includes: a voltage controltransistor connected between a voltage input terminal in which DCvoltage is input and an output terminal; a control circuit whichcontrols the voltage control transistor according to an output feedbackvoltage; and a first external terminal in which an output control signalsupplied from outside to control output voltage is input, wherein, thecontrol circuit further includes: a first error amplifier which outputsa voltage according to an electric potential difference between avoltage divided by a first voltage dividing circuit which divides theoutput voltage of the output terminal and a predetermined referencevoltage; and an output changing circuit which displaces the referencevoltage input in the first error amplifier or the voltage divided by thefirst voltage dividing circuit according to a voltage input in the firstexternal terminal to change the output voltage to a voltage according tothe output control signal.

Preferably, in the semiconductor apparatus for power supply control, theoutput voltage changing circuit includes, a second voltage dividingcircuit which divides the voltage input in the first external terminal,a first transistor and a first resistor element connected in seriesbetween anode from which the voltage divided by the first voltagedividing circuit is taken out and a constant potential point, and asecond error amplifier which outputs voltage according to an electricpotential difference between the voltage divided by the second voltagedividing circuit and the voltage converted by current-voltage conversionby the first resistor element, wherein, the output of the second erroramplifier is applied to a control terminal of the first transistor.

Preferably, in the semiconductor apparatus for power supply control, theoutput voltage changing circuit includes, a third voltage dividingcircuit which divides the reference voltage, a second transistor and asecond resistor element connected in series between a node from whichvoltage divided by the third voltage dividing circuit is taken out and aconstant potential point, and a third error amplifier which outputsvoltage according to an electric potential difference between a voltageinput in the first external terminal and the voltage converted bycurrent-voltage conversion by the second resistor element, wherein theoutput of the third error amplifier is applied to the control terminalof the second transistor.

Preferably, in the semiconductor apparatus for power supply control, theoutput voltage changing circuit includes, a fourth error amplifier inwhich voltage input in the first external terminal is input, a thirdtransistor in which output of the second error amplifier is applied tothe control terminal, a current mirror circuit which is connected to thevoltage input terminal and which transfers an electric current flowingin the third transistor, and a third resistor element connected inseries with the third transistor, wherein, the fourth error amplifieroutputs voltage according to an electric potential difference betweenthe voltage input in the first external terminal and the voltageconverted by current-voltage conversion by the third resistor element tothe control terminal of the third transistor, flows an electric currentaccording to the electric potential difference in the third transistor,and pulls out from or flows in the node from which the voltage dividedby the first voltage dividing circuit is taken out the electric currenttransferred in the current mirror circuit.

Preferably, the semiconductor apparatus for power supply control furtherincludes, a reference voltage source which generates the referencevoltage; a bias circuit which generates an operation electric currentsupplied to the reference voltage source and the first error amplifier;and a second external terminal in which a control signal supplied fromoutside is input to stop an operation of the power supply apparatus,wherein the bias circuit stops the supply of the operation electriccurrent to the reference voltage source and the first error amplifieraccording to the control signal input in the second external terminal.

According to another aspect of the present invention, an output voltagevariable power supply apparatus includes: the semiconductor apparatusfor power supply control; and a control apparatus which outputs a signalinput to the first external terminal or the first external terminal andthe second external terminal, wherein, the output voltage changesaccording to the signal input from the control apparatus to the firstexternal terminal.

Preferably, in the output voltage variable power supply apparatus, aload connected to the output terminal of the semiconductor apparatus forpower supply control is a DC motor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described through the detailed descriptionbelow and the accompanying drawings. Such description and drawingsshould not be construed to limit the present invention.

FIG. 1 is a diagram of a circuit configuration showing a firstembodiment of a series regulator type output voltage variable powersupply apparatus applying the present invention.

FIG. 2 is a graph showing a relation between an output control signalVadj and output voltage Vout in a regulator according to the firstembodiment.

FIG. 3 is a circuit diagram showing an example of an error amplifyingcircuit composing an output control circuit in a regulator according tothe first embodiment.

FIG. 4A and FIG. 4B are block diagrams showing an example of aconfiguration of a power supply system including a regulator accordingto the first embodiment and a microcomputer which controls suchregulator.

FIG. 5A is a waveform diagram showing a signal from the microcomputerand the change in the output voltage according to the power supplysystem shown in FIG. 4A, and FIG. 5B is a waveform diagram showing asignal from the microcomputer and the change in the output voltageaccording to the power supply system shown in FIG. 4B.

FIG. 6 is a circuit diagram showing a modification of an IC composing aregulator applying the first embodiment.

FIG. 7 is a diagram of a circuit configuration showing a secondembodiment of a series regulator type output voltage variable powersupply apparatus applying the present invention.

FIG. 8 is a circuit diagram showing a circuit configuration when asecond current mirror circuit is omitted in a regulator IC according tothe second embodiment shown in FIG. 7.

FIG. 9A is a waveform diagram showing a relation between an on/offcontrol signal ON/OFF, and output control signal Vadj, and an outputvoltage Vout in an output voltage variable power supply apparatus shownin FIG. 7, and FIG. 9B is a waveform diagram showing a relation betweenan on/off control signal ON/OFF, and output control signal Vadj, and anoutput voltage Vout in an output voltage variable power supply apparatusshown in FIG. 8.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A preferable embodiment of the present invention is described withreference to the drawings.

First Embodiment

FIG. 1 shows a first embodiment of a series regulator as an outputvoltage variable power supply apparatus applying the present invention.In FIG. 1, the portion surrounded by a short and long dash line isformed as a semiconductor integrated circuit (regulator IC) 10 on asemiconductor chip such as single crystal silicon. The above functionsas an output voltage variable power supply apparatus which outputs astable DC voltage to a load such as a motor or LED lamp (not shown) byconnecting a condenser Co to an output terminal OUT of the regulator IC10.

As shown in FIG. 1, according to the output voltage variable powersupply apparatus of the present embodiment, P-channel MOS transistor M1to control the voltage (insulated gate electric field effect transistor)is connected between a voltage input terminal IN and an output terminalOUT on which input DC voltage Vin of the regulator IC 10 is applied.Resistors R2 and R1 composing a pressure dividing circuit 12 whichdivides output voltage Vout are connected in series between the outputterminal OUT and a ground line on which ground potential GND is applied.

The voltage of the connection node N1 between the resistors R1 and R2composing the voltage dividing circuit 12 is input as feedback voltageVFB in a non-inverting input terminal of an error amplifier 11 as anerror amplifying circuit which controls a gate terminal of thetransistor M1 for controlling the voltage. Then, the error amplifier 11generates the voltage according to the potential difference betweenoutput feedback voltage VFB and predetermined reference voltage Vref,supplies the voltage to the gate terminal of the transistor M1 forcontrolling the voltage and controls M1 so that the output voltage Voutis a desired electric potential.

In the regulator IC 10 according to the present embodiment, an N-channelMOS transistor M2 and a resistor R3 are connected in series between theconnection node N1 of the resistors R1 and R2 and a grounding point. Inthe regulator IC 10, the output control terminal ADJ is provided as theexternal terminal in which the signal Vadj which controls the outputvoltage Vout supplied from the microcomputer (not shown) is input.Between the terminal ADJ and the grounding point, resistors R4 and R5composing a voltage dividing circuit 14 a which divides the outputcontrol signal Vadj are connected in series.

An error amplifier 14 b is provided as an error amplifying circuit inwhich voltage V3 (voltage of node N3) divided by the voltage dividingcircuit 14 a is to be input and which controls the gate terminal of theMOS transistor M2.

There is negative feedback in the error amplifier 14 b when the voltageV2 of the connection node N2 between the control target MOS transistorM2 and the resistor R3 is input in the inverting input terminal. Withthe imaginary short, the transistor M2 is driven so that an electriccurrent flows in the resistor R3 to make the voltage V2 of the node N2the same as the voltage V3 of the node N3.

Then, the feedback voltage VFB displaced by the above electric currentflowing in the resistor R3 is input in the non-inverting input terminalof the error amplifier 11 which controls the gate terminal of thetransistor M1 for controlling the voltage. With this, the output voltageVout according to the output control signal Vadj is output to the outputterminal OUT of the regulator IC 10. Therefore, the output voltagechanging circuit 14 which changes the voltage of the output voltage Voutaccording to the output controlling signal Vadj is configured with thevoltage dividing circuit 14 a, the error amplifier 14 b and thetransistor M2 and the resistor R3.

The output voltage Vout is represented by the following formula (1).Vout=((R1+R2)/R1)*Vref+(V2/R3)*R2  (1)

The voltage V3 of the node N3 is represented by the following formula(2).V3=(R4/(R4+R5))*Vadj  (2)

Here, V2=V3, and from the above formulas (1) and (2), Vout isrepresented by the following formula (3).Vout=((R1+R2)/R1)*Vref+((R4*R2)/R3*(R4+R5))*Vadj  (3)

According to the above-described formula (3), the output voltage Vout isdetermined by a relative accuracy of the internal resistor, and it ispossible to set the value accurately. The output control signal Vadjinput to the output control terminal ADJ can be set within the outputrange of the D/A conversion circuit which generates the output controlsignal Vadj. Since the gain of the output voltage Vout decreases, thevariation of the output voltage Vout with relation to the accuracy ofthe output control signal Vadj becomes smaller. The variation range ofthe output voltage Vout is Vref to Vin.

FIG. 2 shows an example of a relation between the output control signalVadj and the output voltage Vout in the output voltage variable powersupply apparatus according to the present embodiment. It is possible tounderstand from FIG. 2 that the output voltage Vout is in proportionwith the output control signal Vadj, and the tilt of the Vout−Vadjcharacteristic line A is an almost stable straight line. The tilt can besuitably set by the value of the resistor.

The output voltage Vout when the output control signal Vadj is 0V is “0”from the second term of the above-described formula (3), and therefore,the output voltage Vout is set by the ratio between resistors R1 and R2and the reference voltage Vref. Specifically, for example, when thereference voltage Vref is 1.5V, if the ratio between R1 and R2 is 1:1,the output voltage Vout at Vadj=0V can be set to 3V. With this, forexample, when a power supply apparatus is designed to supply a powersupply voltage to a motor which operates with at least a minimum voltageof 3V, the motor can be surely operated and the number of rotations canbe increased by enhancing the output control signal Vadj.

The regulator IC 10 according to the present embodiment includes areference voltage source 15 which generates a reference voltage Vrefbased on the input voltage Vin, a bias circuit 16 which generates anoperation electric current of the error amplifier 11, and an on/offcontrol terminal CNT as an external terminal in which a signal ON/OFF tocontrol on and off of the bias circuit 16 is input. When the on and offcontrol signal ON/OFF of the low level (0V) is input to the on/offcontrol terminal CNT, the bias circuit 16 stops the supply of theoperation electric current to the reference voltage source 15 and theerror amplifier 11, and the operation of these circuits are stopped.

As the error amplifiers 11 and 14 b, a differential amplifying circuitas shown in FIG. 3 can be used. Such differential amplifying circuitincludes an input unit including transistors M11 and M12 and constantcurrent sources CC1 and CC2, a differential amplifying unit includingdifferential input transistors M13 and M14, active load transistors M15and M16, and constant current source CC3, and output unit including atransistor M17 in which a gate terminal is connected to the output nodeof the differential amplifying unit, and a resistor R10 connectedbetween the source terminal of the transistor M17 and the groundingpoint. The circuit shown in FIG. 3 is one example, and the circuitconfiguration is not limited to the above.

Next, an example of a configuration of the output voltage variable powersupply apparatus which uses the above-described regulator IC 10 andgeneral purpose microcomputer is described with reference to FIG. 4A toFIG. 5B.

FIG. 4A is an example of a configuration of a power supply apparatuswhen a general purpose microcomputer including a D/A conversion circuitis used, and FIG. 4B is an example of a configuration of a power supplyapparatus when a general purpose microcomputer not including a D/Aconversion circuit is used.

When the general purpose microcomputer including a D/A conversioncircuit is used, as shown in FIG. 4A, connection is made so that thesignal D/A output from the output port of the D/A conversion circuitincluded in the microcomputer 20 is input to the external terminal ADJof the regulator IC 10 as the control signal Vadj of the output voltage.Moreover, connection is made so that the ON/OFF signal of the regulatorIC 10 is output from the normal I/O port of the microcomputer 20 to beinput to the on/off control terminal CNT of the regulator 10. Byconfiguring the power supply apparatus to include such connection, asshown in FIG. 5A, it is possible to achieve the output voltage variablepower supply apparatus in which the output voltage Vout can becontinuously changed according to the control signal Vadj input to theoutput control terminal ADJ.

When the general purpose computer not including a D/A conversion circuitis used, as shown in FIG. 4B, connection is made so that the switchingsignal EXC of the output voltage from the I/O port included in themicrocomputer 20 is input to the output control terminal ADJ of theregulator IC 10. Moreover, connection is made so that the ON/OFF signalof the regulator IC 10 is output from the normal I/O port of themicrocomputer 20 to be input to the on/off control terminal CNT of theregulator IC 10. By configuring the power supply apparatus to includesuch connection, as shown in FIG. 5B, it is possible to achieve theoutput voltage variable power supply apparatus which is able to changein stages the output voltage Vout according to the switching signal EXCinput to the output control terminal ADJ.

According to the regulator IC 10 of the present embodiment, it ispossible to achieve the output voltage variable power supply apparatuswhich does not use the external component of the IC and which is able tochange the output voltage Vout by only the control signal Vadj or theEXC input to the output control terminal ADJ. The output voltage isdetermined by the accuracy of the reference voltage and the ratio of theinternal resistor. With this, the accuracy and the temperaturecharacteristics become good. In addition, the variable input voltagerange becomes large and the variation accuracy of the input voltagebecomes small. The feedback voltage is displaced and the output voltageis changed by the voltage-current conversion by the error amplifier, andtherefore, a variable power supply apparatus in which the influencereceived by the power supply noise is small can be achieved.

When the D/A conversion function included in the microcomputer is usedto generate the output control signal, the output voltage can be changedby only changing the software. In addition, the output voltage can beswitched in two stages by the I/O function of the microcomputer.

According to the regulator IC 10 of the present embodiment, the on/offcontrol terminal CNT to input the ON/OFF signal to stop the operation ofthe IC is provided. However, such on/off control terminal CNT can beomitted. When the on/off control terminal CNT is omitted, the regulatorIC 10 can be made with four terminals. Therefore, the package can bemade smaller, and this can reduce space and costs. The regulator IC 10as described above uses the MOS transistor as the voltage controltransistor M1 and the transistor M2 included in the output voltagechanging circuit. Alternatively, the bipolar transistor can be usedinstead of the MOS transistor.

(Modification)

Next, the modification of the regulator IC 10 of the above-describedembodiment is described with reference to FIG. 6.

According to the modification shown in FIG. 6, the resistors R4 and R5included in the voltage dividing circuit 14 a connected to the outputcontrol terminal ADJ of the regulator IC 10 in the above-describedembodiment is omitted. Instead, a voltage dividing circuit 17 isprovided, and the voltage dividing circuit 17 includes resistors R6 andR7 which divide the voltage of the reference voltage Vref generated bythe reference voltage source 15. The voltage Vref′ divided by theresistors R6 and R7 is input to the error amplifier 11. Between theconnection node N4 for the resistors R6 and R7 and the grounding point,the MOS transistors M2 and the resistor R3 included in the outputvoltage changing circuit 14 are connected in series, and the outputcontrol signal Vadj input in the output control terminal ADJ is directlyinput to the non-inverting input terminal of the error amplifier 14 b.

In the regulator using the regulator IC of the modification shown inFIG. 6, the voltage Vref′ of the node N4 is represented by the followingformula (4).Vref′=(1/R6+R7)*(R6*Vref−(R6*R7/R3)*Vadj)  (4).Therefore, the output voltage Vout is represented by the followingformula.

$\begin{matrix}\begin{matrix}{{Vout} = {\left( {{\left( {{R\; 1} + {R\; 2}} \right)/R}\; 1} \right)*{Vef}^{\mspace{11mu}\prime}}} \\{= {\left( {{\left( {{R\; 1} + {R\; 2}} \right)/R}\; 1*\left( {{R\; 6} + {R\; 7}} \right)} \right)*\left( {{R\; 6*{Vref}} -} \right.}} \\\left. {\left( {R\; 6*R\;{7/R}\; 3} \right)*{Vadj}} \right)\end{matrix} & (5)\end{matrix}$

It is possible to understand from the above-described formula (5) thatthe output voltage Vout is determined by the relative accuracy of theinternal resistor, and this can be set accurately. Moreover, by changingthe control signal Vadj input to the output control terminal ADJ, theoutput voltage Vout can be changed.

Second Embodiment

FIG. 7 shows a second embodiment of the regulator IC 10 including aseries regulator as the output voltage variable power supply apparatusapplying the present invention.

Instead of providing the voltage dividing circuit 14 a of the outputvoltage changing circuit 14 in the first embodiment shown in FIG. 1, theoutput voltage variation power supply apparatus according to the presentembodiment includes a first current mirror circuit 17 a includingtransistors Tr1 and Tr2 connecting the base terminals of each other anda second current mirror circuit 17B including transistors Tr1 and Tr4connecting the base terminals of each other as shown in FIG. 7.

The base terminal and the collector terminal of the transistors Tr1 andTr3 are connected to function as the current-voltage conversion element.The converted voltage is applied to the transistors Tr2 and Tr4. Withthis, the electric current according to an emitter size ratio of the Tr1and Tr2 and an emitter size ratio of the Tr3 and Tr4 flow in each of thetransistors Tr2 and Tr4.

The transistor M2 as the voltage-current conversion element driven bythe error amplifier 14 b is not connected with the connection node ofthe resistors R2 and R1 included in the voltage dividing circuit 12which generates the feedback voltage VFB. The transistor M2 is connectedin series with the transistor Tr1 included in the first current mirrorcircuit 17A. The electric current of the transistor M2 is transferredwith the current mirror circuits 17A and 17B, and the electric currentis pulled out from the connection node N1 of the resistors R2 and R1.

Although not limited, the second embodiment describes the regulator IC10 configured with a bipolar transistor. However, an MOS transistor(P-channel MOS and N-channel MOS) as in the first embodiment may beused. The other components of the configuration is the same as theregulator IC as described in the first embodiment.

In the regulator using the regulator IC of the second embodiment shownin FIG. 7, when the current ratio between the current mirror circuit 17Aand 17B is set to be 1:1, the output voltage Vout is represented asfollows.Vout=((R1+R2)/R1)*Vref+(Vadj/R3)*R2  (6)

Therefore, in the output voltage variation power supply apparatusaccording to the present embodiment, similar to the first embodiment, byapplying any voltage (control signal Vadj) to the output controlterminal ADJ, any output voltage can be set, and the output voltage Voutcan be changed linearly according to the applied voltage on the outputcontrol terminal ADJ.

Specifically, FIG. 9A shows the relation between the input signal ON/OFFto the on/off control terminal CNT in the output voltage variation powersupply apparatus according to the present embodiment, the control signalVadj input to the output control terminal ADJ, and the output voltageVout. It is possible to understand from FIG. 9A that when the controlsignal Vadj is changed within the range of 0 to 3.3V, the output voltageVout can be changed in the range of V1 to Vin. The variable range of thecontrol signal Vadj being 0 to 3.3V is one example, and the presentembodiment is not limited to the above.

According to the output voltage variable power supply apparatus of thefirst embodiment shown in FIG. 1, a voltage dividing circuit 14 a(resistors R5, R4) to divide the input voltage (Vadj) is provided in theoutput voltage changing circuit 14 to make the input range of thevoltage (control signal Vadj) to the output control terminal ADJ larger,and the electric potential V3 of the connection node N3 of the voltagedividing circuit 14 a needs to be set to equal to or less than Vref−Vds(M2) including variation. The voltage (Vadj) of the output controlterminal ADJ is compressed with the voltage dividing circuit 14 a andthe output voltage Vout is changed to the desired voltage range. Sincethe electric potential V3 of the node N3 is multiplied by the gain ofthe output voltage changing circuit 14, the variation in the resistingratio of the resistors R5 and R4 of the voltage dividing circuit 14 agreatly influences the output voltage Vout.

According to the second embodiment, the voltage (Vadj) of the outputcontrol terminal ADJ is not compressed in the voltage dividing circuit14 a. Therefore, the control accuracy of the output voltage Vout by thecontrol signal Vadj is enhanced compared to the output voltage variablepower supply apparatus according to the first embodiment. According tothe second embodiment, the variable range of the output voltage Vout canbe changed with not only the resisting value of the resistor R3 of theoutput voltage changing circuit 14 but also the electric current ratioof the current mirror circuit 17A and 17B. With this, there is theadvantage that the freedom of design is enhanced.

Further, according to the second embodiment, the variable control logicof the output voltage Vout by the control signal Vadj can be switched bythe existence of the current mirror circuit 17B.

Specifically, the transistors Tr1 and Tr2 included in the current mirrorcircuit 17A and the transistors Tr3 and Tr4 included in the currentmirror circuit 17B can be made on the chip of the regulator IC inadvance. With a mask option, the connection lines between thetransistors Tr2 and Tr3 are switched to the connection lines between thetransistor Tr2 and the node 3 or the forming position of the throughhole with relation to the lines from the node N3 to the input terminalof the error amplifier 11 is switched. With this, it is possible toobtain a circuit provided with only the current mirror circuit 17A or acircuit provided with both current mirror circuits 17A and 17B.

FIG. 8 shows a circuit diagram of the regulator IC 10 included in theseries regulator in the second embodiment. In the regulator IC 10, thesecond current mirror circuit 17B is omitted in the regulator IC 10 ofthe second embodiment shown in FIG. 7 with a similar method. Thecollector terminal of the transistor Tr2 included in the first currentmirror circuit 17A is connected to the connection node N1 of theresistors R2 and R1 included in the voltage dividing circuit 12. Thecurrent of the transistor M2 transferred in the current mirror circuit17A flows in the connection node N1 of the resistors R2 and R1.

In the regulator IC 10 shown in FIG. 8, when the electric current ratioof the current mirror circuit 17A is set to 1:1, the output voltage Voutis represented by the following formula.Vout=((R1+R2)/R1)*Vref−(R1*Vadj/R3)  (7)

It is possible to understand from this formula that the logic isopposite of the first embodiment, that is, as the control signal Vadjbecomes lower, the output voltage Vout becomes higher.

FIG. 9B shows the relation between the input signal ON/OFF to the on/offcontrol terminal CNT in the output voltage variable apparatus of themodification, the control signal Vadj input to the output controlterminal ADJ and the output voltage Vout. It is possible to understandfrom FIG. 9B that when the control signal Vadj changes within the rangeof 0 to 3.3V for example, the output voltage Vout changes within therange of Vin to V1. The variable range of the control signal Vadj being0 to 3.3V is one example, and the present embodiment is not limited tothe above.

When the user desires to configure the power supply apparatus to changethe control logic of the output voltage Vout, that is, instead of theoutput voltage Vout becoming high when the control signal Vadj becomeshigh, the output voltage Vout becomes high when the control signal Vadjis low, it is necessary to provide a separate amplifier such as theinverting amplifying circuit in the stage before the error amplifier 14b in the output voltage variation power supply apparatus of the firstembodiment. According to the modification, the control logic can bechanged by omitting only the current mirror circuit 17B. The currentmirror circuits 17A and 17B in FIG. 7 and FIG. 8 are not limited tothose illustrated and may be a type in another circuit format such as aWilson type or a base current compensation type.

The present invention is described in detail based on the embodiments ofthe present invention, but the present invention is not limited to theembodiments shown. For example, the first and second embodimentsdescribe using a D/A conversion function included in the microcomputerto continuously change the output voltage Vout. However, other than theD/A output, a bleeder resisting circuit including a variable resistorcan be used. The voltage dividing circuit (resistors R1, R2) 12 whichgenerates the feedback voltage VFB of the output voltage and theresistor R3 may be connected as an external element of the regulator IC10.

According to the present embodiment, the present invention is applied tothe output voltage variable power supply apparatus in series regulatortype, but the present invention can be applied to the power supplyapparatus in a shunt regulator type.

According to one aspect of the present invention, there is asemiconductor apparatus for power supply control including: a voltagecontrol transistor connected between a voltage input terminal in whichDC voltage is input and an output terminal; a control circuit whichcontrols the voltage control transistor according to an output feedbackvoltage; and a first external terminal in which an output control signalsupplied from outside to control output voltage is input, wherein, thecontrol circuit further includes: a first error amplifier which outputsa voltage according to an electric potential difference between avoltage divided by a first voltage dividing circuit which divides theoutput voltage of the output terminal and a predetermined referencevoltage; and an output changing circuit which displaces the referencevoltage input in the first error amplifier or the voltage divided by thefirst voltage dividing circuit according to a voltage input in the firstexternal terminal to change the output voltage to a voltage according tothe output control signal.

According to the semiconductor apparatus for power supply control andthe output voltage variable power supply apparatus including the aboveconfiguration, the output voltage can be changed linearly with theoutput control signal from outside.

Moreover, the external element is not necessary. Since the outputvoltage is determined by the accuracy of the reference voltage and theratio of the internal resistor, the accuracy and the temperaturecharacteristics are preferable, the variable input voltage range becomeslarge, and the variation accuracy of the input voltage becomes small.Further, when the output control signal is generated using the D/Aconversion function included in the microcomputer, the output voltage isvariable by only changing the software.

Preferably, in the semiconductor apparatus for power supply control, theoutput voltage changing circuit includes, a second voltage dividingcircuit which divides the voltage input in the first external terminal,a first transistor and a first resistor element connected in seriesbetween a node from which the voltage divided by the first voltagedividing circuit is taken out and a constant potential point, and asecond error amplifier which outputs voltage according to an electricpotential difference between the voltage divided by the second voltagedividing circuit and the voltage converted by current-voltage conversionby the first resistor element, wherein, the output of the second erroramplifier is applied to a control terminal of the first transistor.

Preferably, in the semiconductor apparatus for power supply control, theoutput voltage changing circuit includes, a third voltage dividingcircuit which divides the reference voltage, a second transistor and asecond resistor element connected in series between a node from whichvoltage divided by the third voltage dividing circuit is taken out and aconstant potential point, and a third error amplifier which outputsvoltage according to an electric potential difference between a voltageinput in the first external terminal and the voltage converted bycurrent-voltage conversion by the second resistor element, wherein theoutput of the third error amplifier is applied to the control terminalof the second transistor.

According to the above-described configuration, the reference voltage orthe feedback voltage is displaced with the voltage-electric currentconversion by the error amplifier, and the output voltage is changed.Therefore the variable power supply apparatus in which the influence ofthe power supply noise is small can be obtained.

Preferably, in the semiconductor apparatus for power supply control, theoutput voltage changing circuit includes, a fourth error amplifier inwhich voltage input in the first external terminal is input, a thirdtransistor in which output of the second error amplifier is applied tothe control terminal, a current mirror circuit which is connected to thevoltage input terminal and which transfers an electric current flowingin the third transistor, and a third resistor element connected inseries with the third transistor, wherein, the fourth error amplifieroutputs voltage according to an electric potential difference betweenthe voltage input in the first external terminal and the voltageconverted by current-voltage conversion by the third resistor element tothe control terminal of the third transistor, flows an electric currentaccording to the electric potential difference in the third transistor,and pulls out from or flows in the node from which the voltage dividedby the first voltage dividing circuit is taken out the electric currenttransferred in the current mirror circuit.

According to the above configuration, the output voltage is changedlinearly by the output control signal input in the first externalterminal.

The output control signal input in the first external terminal is notcompressed by the pressure dividing circuit, and the control accuracy ofthe output voltage by the control signal is enhanced. In addition, thevariable range of the output voltage can be changed by not only theresisting value of the resistor element included in the output voltagechanging circuit but also by changing the electric current ratio of thecurrent mirror circuit. Therefore, the freedom of design is enhanced.

Further, the variable control logic of the output voltage by the outputcontrol signal input in the first external terminal can be switched bychanging the configuration of the current mirror circuit.

Preferably, the semiconductor apparatus for power supply control furtherincludes, a reference voltage source which generates the referencevoltage; a bias circuit which generates an operation electric currentsupplied to the reference voltage source and the first error amplifier;and a second external terminal in which a control signal supplied fromoutside is input to stop an operation of the power supply apparatus,wherein the bias circuit stops the supply of the operation electriccurrent to the reference voltage source and the first error amplifieraccording to the control signal input in the second external terminal.

According to the above configuration, the operation of the semiconductorapparatus for power supply control can be stopped with the controlsignal from outside, and the power supply apparatus can be stopped bythe I/O function of the microcomputer.

According to another aspect of the present invention, an output voltagevariable power supply apparatus includes: the semiconductor apparatusfor power supply control; and a control apparatus which outputs a signalinput to the first external terminal or the first external terminal andthe second external terminal, wherein, the output voltage changesaccording to the signal input from the control apparatus to the firstexternal terminal.

According to the output voltage variable power supply apparatusincluding the above configuration, the output voltage can be linearlychanged by the input of the control signal to the first externalterminal from the outside, and when the second external terminal isprovided, the operation of the semiconductor apparatus for power supplycontrol can be stopped with the control signal from outside, and thepower supply apparatus can be stopped with the I/O function of themicrocomputer.

According to the semiconductor apparatus for the power supply controland the output voltage variable power supply apparatus according to thepresent invention, the output voltage can be changed linearly withoutincreasing the number of elements and the number of components.According to the present invention, a general purpose microcomputer canbe used to easily control the output voltage in the semiconductorapparatus for power supply control and the output voltage variable powersupply apparatus.

The embodiments described above of the present invention should beconstrued for mere illustrative purposes, not for limitation. Thepresent invention is not limitedly applied to the above-describedembodiments, and appropriate modifications or alterations of theinvention can be made within the scope without departing from the spiritof the invention.

What is claimed is:
 1. A semiconductor apparatus for power supplycontrol, comprising: a voltage control transistor connected between avoltage input terminal in which DC voltage is input and an outputterminal; a control circuit which controls the voltage controltransistor according to an output feedback voltage; and a first externalterminal in which an output control signal supplied from outside tocontrol an output voltage is input, wherein the control circuitincludes: a first error amplifier which outputs a voltage according toan electric potential difference between a voltage divided by a firstvoltage dividing circuit which divides the output voltage of the outputterminal and a predetermined reference voltage; and an output changingcircuit which includes a second error amplifier in which a voltage inputin the first external terminal is input, a transistor in which an outputof the second error amplifier is applied to a control terminal thereof,and a current mirror circuit which is connected to the voltage inputterminal and which transfers an electric current flowing in thetransistor, wherein the output changing circuit displaces the voltagedivided by the first voltage dividing circuit input in the first erroramplifier according to a voltage input in the first external terminal tochange the output voltage to a voltage according to the output controlsignal.
 2. The semiconductor apparatus for power supply controlaccording to claim 1, wherein the output changing circuit includes aresistor element connected in series with a transistor, wherein thesecond error amplifier outputs voltage according to an electricpotential difference between the voltage input in the first externalterminal and a voltage converted by current-voltage conversion by theresistor element to the control terminal of the transistor, flows anelectric current according to the electric potential difference in thetransistor, and flows, in a node from which the voltage divided by thefirst voltage dividing circuit is taken out, the electric currenttransferred in the current mirror circuit.
 3. The semiconductorapparatus for power supply control according to claim 1, furthercomprising: a reference voltage source which generates the referencevoltage; a bias circuit which generates an operation electric currentsupplied to the reference voltage source and the first error amplifier;and a second external terminal in which a control signal supplied fromoutside is input to stop an operation of the power supply apparatus,wherein the bias circuit stops the supply of the operation electriccurrent to the reference voltage source and the first error amplifieraccording to the control signal input in the second external terminal.4. An output voltage variable power supply apparatus comprising: thesemiconductor apparatus for power supply control according to claim 1;and a control apparatus which outputs a signal input to the firstexternal terminal or to the first external terminal and the secondexternal terminal, wherein the output voltage changes according to thesignal input from the control apparatus to the first external terminal.5. The output voltage variable power supply apparatus according to claim4, wherein a load connected to the output terminal of the semiconductorapparatus for power supply control is a DC motor.
 6. A semiconductorapparatus for power supply control, comprising: a voltage controltransistor connected between a voltage input terminal in which DCvoltage is input and an output terminal; a control circuit whichcontrols the voltage control transistor according to an output feedbackvoltage; and a first external terminal in which an output control signalsupplied from outside to control an output voltage is input, wherein thecontrol circuit includes: a first error amplifier which outputs avoltage according to an electric potential difference between a voltagedivided by a first voltage dividing circuit which divides the outputvoltage of the output terminal and a predetermined reference voltage;and an output changing circuit which includes a second error amplifierin which a voltage input in the first external terminal is input, atransistor in which an output of the second error amplifier is appliedto a control terminal thereof, and a current mirror circuit which isconnected to the voltage input terminal and which transfers an electriccurrent flowing in the transistor, wherein the output changing circuitflows the electric current transferred in the current mirror circuit toa node in which the voltage divided by the first voltage dividingcircuit is taken out and displaces the voltage divided by the firstvoltage dividing circuit input in the first error amplifier to changethe output voltage.
 7. The semiconductor apparatus for power supplycontrol according to claim 6, further comprising: a reference voltagesource which generates the reference voltage; a bias circuit whichgenerates an operation electric current supplied to the referencevoltage source and the first error amplifier; and a second externalterminal in which a control signal supplied from outside is input tostop an operation of the power supply apparatus, wherein the biascircuit stops the supply of the operation electric current to thereference voltage source and the first error amplifier according to thecontrol signal input in the second external terminal.
 8. An outputvoltage variable power supply apparatus comprising: the semiconductorapparatus for power supply control according to claim 6; and a controlapparatus which outputs a signal input to the first external terminal orto the first external terminal and the second external terminal, whereinthe output voltage changes according to the signal input from thecontrol apparatus to the first external terminal.
 9. The output voltagevariable power supply apparatus according to claim 8, wherein a loadconnected to the output terminal of the semiconductor apparatus forpower supply control is a DC motor.
 10. A semiconductor apparatus forpower supply control comprising: a voltage control transistor connectedbetween a voltage input terminal in which DC voltage is input and anoutput terminal; a control circuit which controls the voltage controltransistor according to an output feedback voltage; and a first externalterminal in which an output control signal supplied from outside tocontrol an output voltage is input, wherein the control circuitincludes: a first error amplifier which outputs a voltage according toan electric potential difference between a voltage divided by a firstvoltage dividing circuit which divides the output voltage of the outputterminal and a predetermined reference voltage; and an output changingcircuit which includes a second error amplifier in which voltage inputin the first external terminal is input, a transistor in which an outputof the second error amplifier is applied to a control terminal thereof,and a current mirror circuit which is connected to the voltage inputterminal and which transfers an electric current flowing in thetransistor, wherein the output changing circuit performs linearvariation on the output voltage with a negative coefficient according toa voltage input in the first external terminal.
 11. The semiconductorapparatus for power supply control according to claim 10, furthercomprising: a reference voltage source which generates the referencevoltage; a bias circuit which generates an operation electric currentsupplied to the reference voltage source and the first error amplifier;and a second external terminal in which a control signal supplied fromoutside is input to stop an operation of the power supply apparatus,wherein the bias circuit stops the supply of the operation electriccurrent to the reference voltage source and the first error amplifieraccording to the control signal input in the second external terminal.12. An output voltage variable power supply apparatus comprising: thesemiconductor apparatus for power supply control according to claim 10;and a control apparatus which outputs a signal input to the firstexternal terminal or to the first external terminal and the secondexternal terminal, wherein the output voltage changes according to thesignal input from the control apparatus to the first external terminal.13. The output voltage variable power supply apparatus according toclaim 12, wherein a load connected to the output terminal of thesemiconductor apparatus for power supply control is a DC motor.